Managing Acute and Chronic Laminitis

To a packed room of veterinarians at the 2007 American Association of Equine Practitioners Convention in Orlando, Fla., Jim Belknap, DVM, PhD, Dipl. ACVS, an associate professor of veterinary clinical sciences from The Ohio State University's Galbreath Equine Center, and Rob Boswell, DVM, a practitioner with Palm Beach Equine Clinic in Wellington, Fla., opened the table topic discussion about prevention and treatment of laminitis.

Belknap (who co-hosted TheHorse.com's Webinar on Understanding Laminitis) said the latest research points to laminitis as an intense inflammatory injury of the foot, and it is no longer believed to be solely a blood flow problem. It is known that even though a horse with imminent laminitis might look normal and show no lameness, inflammatory mediators are already elevated by up to 1,000-fold in the laminae.

With that in mind, Belknap is an advocate of very high levels of anti-inflammatory medications (500 mg three times per day of flunixin meglumine, or Banamine) within the first 72 hours of insult (a cause of laminitis) or onset. He said he realized this high dose is more likely to lead to some gastrointestinal (GI) ulceration and, thus, it should not be used on every horse. But he stressed that it is critical to get foot inflammation under control, so ulceration might be the lesser of two evils. Once the acute stage has settled down, it might be desirable to switch to phenylbutazone for better pain relief.

Ice might be beneficial for the same reason that hypothermia is used in some types of inflammatory injury in human medicine: hypothermia is anti-inflammatory and slows the metabolic rate (i.e., enzyme activity) of injured tissue. There could be great benefit to immediately ice the feet to decrease activity of deleterious enzymes such as matrix metalloproteinases and to decrease inflammation. Studies show the best means of cooling the feet is by using a bucket arrangement or wrapping the hoof in a 5-liter plastic bag or truck tire inner tube filled with ice and water. Refresh the ice continually as needed. The discussion facilitators stressed that no harm can come of keeping feet in ice for 72 hours--as much ice therapy as possible is desirable in averting the inflammatory effects related to acute laminitis. After 72 hours, no ice is necessary and, in fact, it might be counterproductive by softening the foot too much. The horse should not be walked during the acute phase.

DMSO (dimethyl sulfoxide) is a commonly employed drug for laminitis treatment, but there is very little research supporting its use. In an already-laminitic horse, DMSO might have anti-inflammatory properties due to its being a superoxide radical scavenger (it binds to radicals and inactivates them), and it might work as a vasodilator. It can be given either orally or intravenously (IV) with good absorption.

Equioxx is a new non-steroidal anti-inflammatory drug (NSAID) that targets COX-2 inflammatory mediators. Belknap advised that this drug needs five to seven days to reach a steady state of effect, but if it's initially given at a triple dose, the steady state can be reached in 24 hours. Until scientists perform research on its effect in the early stages of laminitis, it might be best used on nonacute cases due to concerns about its potential to exacerbate vascular events (such as Vioxx did in humans at risk) in the at-risk horse or in the acute case of laminitis.

Equioxx should be advantageous in chronic cases, as there should be fewer side effects due to a lowered incidence of GI ulceration or kidney lesions when compared to other NSAIDs. However, it was also mentioned that COX-2 mediators are needed to heal gastric ulcers, so there is some concern on giving the drug to horses known to have GI ulcers.

Blood flow might not play as predominant a role as once thought, so vasodilator therapy is not necessarily as important as some other treatment choices. Acepromazine only opens vascular beds for about 40 minutes following intramuscular (IM) administration, so if given, it should be administered at least four times a day. Another possible vasodilator to use is IV lidocaine.

Belknap and Boswell said they felt a single dose of dexamethasone in a horse at risk of laminitis might help decrease inflammation in the feet, but the vets are resistant to use it due to potential litigation regarding steroid use and laminitis.

Supporting the Hoof

The facilitators and audience discussed foot support. Boswell prefers a two-part putty mixture material placed generously from the tip of the frog to the back of the frog and into the sulci (grooves in the sides of the frog). This recruits the frog and the sulci for support. There was mention that "Soft-Ride" pads give a horse with acute laminitis a good measure of relief, but these pads only contact the frog, so it helps to also use impression material within the sulci.

Lidocaine nerve blocking of the front feet on the initial visit allows assessment of any hind limb involvement, shoe removal, and radiographs. Belknap suggests that veterinarians use lidocaine for the nerve block due to its short duration of action. Shoes left in place could place too much pressure on the hoof wall and laminae. Removal of the shoes also allows the practitioner to obtain good X ray images to evaluate the internal components of each hoof. Prognosis of foot health and integrity is achieved by comparative views of radiographs (both lateral and D-P, or dorsopalmar, views) taken during the initial 35 days of a laminitis event. Measurements of the distance from the dorsal hoof wall to the dorsal border of the coffin bone assist in evaluating the integrity of the laminae within the hoof capsule and helping determine if there is any displacement or rotation of the coffin bone.

Boswell suggests serial weekly radiographs for four weeks. If there is a 25-30% decrease in sole depth during this time, this is not considered a good prognosis and the laminitis is likely terminal. If there is less than 6-7 mm of sole, treatment might fail to alleviate the crisis. If a horse is not progressing well despite aggressive therapy, a venogram might be helpful to determine the circulation in the front of the hoof. If circulation is absent, euthanasia might be indicated. However, not all veterinarians agree, and it was stated that some horses have been saved that appeared to have no chance on venogram results.

If the shoes are left on, the back of each foot should be filled with cushion support substance (such as two-part putty) from the tip of the frog to the back of the foot. The hoof should be placed on the ground so the material fills the spaces within the frog and any extra oozes out that would have caused excess pressure.

The shoes are constructed from a wood block and can be customized in several ways, such as by adding/removing layers or routing out specific areas to alleviate pressure.

In the early stages, a horse undergoing rotation can be placed in a temporary raised-heel shoe, such as the Nanric Ultimate (taped on), but both practitioners recommend unscrewing one wedge from this shoe to make it shorter in horses whose coffin bones have both rotated and undergone sinking. The objective is to stabilize and derotate the coffin bone as much as possible to relieve forces, while providing support to internal structures of the foot. Both clinicians emphasized that it is important to watch the horse's response to shoeing, and they should realize that there is not one type of foot support that works for every horse.

The discussion continued onto chronic laminitis, noting that an affected horse has a mechanical problem that can't be fixed chemically by this point in the disease. The best approach is using special shoes. Audience discussion centered around the wooden clog shoe, using either a homemade shoe made of 1-1/8" plywood, beveled 45 degrees all the way around, or the commercially available EDSS (Equine Digit Support System) product. These are screwed in on the side of the hoof wall, and just enough cushion impression material is placed in the frog area to give relief without too much pressure. Such a shoe absorbs concussion and allows the horse to adjust how he wants to stand, possibly more so than with other shoeing options. Belknap and Boswell pointed out that they use many different types of shoes in the chronic cases, and one shoe does not work on all cases.

Belknap has noticed that previously 10% of laminitis cases were in horses with pasture-associated obesity; now this has increased to 60-70% of cases. He cannot find an explanation for that trend, nor did anyone in the audience have any suggestions.

About the Author

Nancy S. Loving, DVM, owns Loving Equine Clinic in Boulder, Colorado,
and has a special interest in managing the care of sport horses. Her book, All Horse Systems Go, is a comprehensive veterinary care and conditioning resource in full color that covers all facets of horse care. She has also authored the books Go the Distance as a resource for endurance horse owners, Conformation and Performance, and First Aid for Horse and Rider in addition to many veterinary articles for both horse owner and professional audiences.

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